Diurnal variations of stratospheric ozone measured by ground-based microwave remote sensing at the Mauna Loa NDACC site: measurement validation and GEOSCCM model comparison

Abstract

Abstract. There is presently renewed interest in diurnal variations of stratospheric and mesospheric ozone for the purpose of supporting homogenization of records of various ozone measurements that are limited by the technique employed to being made at certain times of day. We have made such measurements for 19 years using a passive microwave remote sensing technique at the Mauna Loa Observatory (MLO) in Hawaii, which is a primary station in the Network for Detection of Atmospheric Composition Change (NDACC). We have recently reprocessed these data with hourly time resolution to study diurnal variations. We inspected differences between pairs of the ozone spectra (e.g., day and night) from which the ozone profiles are derived to determine the extent to which they may be contaminated by diurnally varying systematic instrumental or measurement effects. These are small, and we have reduced them further by selecting data that meet certain criteria that we established. We have calculated differences between profiles measured at different times: morning-night, afternoon-night, and morning-afternoon and have intercompared these with like profiles derived from the Aura Microwave Limb Sounder (Aura-MLS), the Upper Atmosphere Research Satellite Microwave Limb Sounder (UARS-MLS), the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES), and Solar Backscatter Ultraviolet version 2 (SBUV/2) measurements. Differences between averages of coincident profiles are typically < 1.5 % of typical nighttime values over most of the covered altitude range with some exceptions. We calculated averages of ozone values for each hour from the Mauna Loa microwave data, and normalized these to the average for the first hour after midnight for comparison with corresponding values calculated with the Goddard Earth Observing System Chemistry Climate Model (GEOSCCM). We found that the measurements and model output mostly agree to better than 1.5 % of the midnight value, with one noteworthy exception: The measured morning-night values are significantly (2-3 %) higher than the modeled ones from 3.2 to 1.8 hPa (∼ 39-43 km), and there is evidence that the measured values are increasing compared to the modeled values before sunrise in this region.

A climatology of the diurnal variations in stratospheric and mesospheric ozone over Bern, Switzerland

“…At 1.42 hPa, GROMOS measures a decrease in ozone during daytime (−5 to −7 %), while models already switched to a slight increase of daytime ozone. The Mauna Loa microwave instrument (March average of 1996-2012) also shows a decrease of −5 % at 1.3 hPa, supporting our measurements (Parrish et al, 2012). However we should keep in mind that both radiometers have a lower vertical resolution than the models.…”

Retrieving vertical ozone profiles from measurements of global spectral irradiance

“…For example, when MLS 2 data are from the observation period close to local solar noon (14:11 to 15:10 UTC) and MLS 1 data are measured close to sunrise (05:28 to 06:26 UTC), MLS 2 data for layers 7-9 have a high bias of 3-6 % relative to the MLS 1 data set, while MLS 2 data for Layer 10 have a low bias of 8 %. This timeof-day dependency and its variation with altitude is by and large consistent with diurnal variations of the ozone profile measured by various instruments at Mauna Loa, Hawaii (Parrish et al, 2014), and by a microwave radiometer at Bern, Switzerland (Studer et al, 2014). This suggests that the timeof-day effect observed at Summit is caused by actual diurnal changes of the ozone profile rather than potential timedependent systematic errors in the MLS data set.…”

Past changes in the vertical distribution of ozone – Part 3: Analysis and interpretation of trends

“…In addition, sampling errors can arise when the sampling frequency changes, especially when this is aliased with cycles in ozone, e.g. annually (Damadeo et al, 2014) and diurnally (Sakazaki et al, 2013;Parrish et al, 2014). All these factors serve to confuse and complicate the picture.…”